1. Field of the Invention
Exemplary embodiments of the present invention relate to a communication system, and more particularly, to an apparatus and a method for coding voice and audio signals using a code excited linear prediction (hereinafter, referred to as ‘CELP’) coding method in a communication system.
2. Description of Related Art
In a communication system, researches for providing services having various qualities of services (hereinafter, referred to as QoSs) to users at a high transmission rate have been actively conducted. The communication system has proposed methods for transmitting data having various types of QoSs at high speed through a limited resource. Recently, as a method for compressing and transmitting voice and audio signals in a network so as to cope with development of a network and the increase in a user demand, methods for compressing and reconstructing a pulse code modulation (hereinafter, referred to as ‘PCM’) signal have been proposed. Many voice/audio codecs for compressing and reconstructing the PCM signal have been developed.
Meanwhile, as an example of the voice/audio codec, recent codecs such as ITU-T, G729.1, G.718, and the like support multi bit rates using an embedded structure and implement a high compression rate based on the CELP technology that models a process of generating voice and audio signals in a low bit rate of the multi bit rates. In addition, residual signals of the voice and audio signals in a high bit rate of the multi bit rates are quantized by transforming a time domain into a frequency domain based on a modified discrete cosine transform (hereinafter, referred to as ‘MDCT’) or a discrete Fourier transform (hereinafter, referred to as ‘DFT’).
Here, the CELP technology is a technology designed to be more suitable for voice rather than for music in the voice and audio signals and makes characteristics of the residual signals that are a difference between an original sound and a synchronized signal coded by the CELP technology different. That is, in the case of voice, the CELP technology properly represents a formant having a large frequency size and a pitch, but in the case of music, does not properly represent a formant and a pitch, such that a larger frequency component remains in the residual signals. That is, in the CELP technology, even in the case of the same voice, in the signal having the uniformly distributed frequency due to the accurately represented formant and pitch as well as the signal due to the inaccurately represented formant and pitch as described above, the coefficient having a large frequency may appear in the residual signals.
However, in the current communication system, when the voice and audio signals are coded by the CELP technology, that is, the CELP coding method, as described above, a detailed method for normally processing the residual signals of the voice and audio signals has not yet been proposed. In particular, the residual signals are not normally processed to degrade the coding performance of the voice and audio signals based on the CELP coding method, such that the high quality of services may be provided to users.
Therefore, a need exists for a method for coding voice and audio signals based on a CELP coding method so as to provide a high quality of voice and audio services in a communication system.